The present application claims priority on Japanese Patent Application No. 2010-129224, filed Jun. 4, 2010, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a seat back frame for a vehicle. The seat back frame comprises a feature such that a movement of an upper body of a passenger is controlled when an impact is entered from a rear part of the vehicle.
2. Description of the Related Art
A seat back frame for a vehicle is suggested in Japanese Unexamined Patent
Application, First Publication No. H10-181400 (hereinafter referred to as Patent Document 1). This seat back frame is provided at a position corresponding to an upper portion of the pelvis of a passenger seated on a seat. In order to quickly reduce the space between the head part of the passenger and the head rest when an impact load is entered from a rear part of the vehicle, the seat back frame comprises an upper pelvis supporting unit which supports the passenger from a back side. The seat back frame also comprises a chest part supporting unit which is provided at a position corresponding to a chest part of the passenger.
According to this seat back frame disclosed in Patent Document 1, a crushing load of the chest part supporting unit is set to be lower than a crushing load of the upper pelvis supporting unit. Therefore, when an impact enters from a rear part of the vehicle, the chest part supporting unit is first crushed. Then, the upper pelvis supporting unit is crushed. Therefore, the chest part and the head part of the passenger tilts towards a rear direction, with a hip part (upper portion of the pelvis) being a fulcrum point. As a result, the head part approaches the head rest at an early stage.
However, according to the configuration disclosed in Patent Document 1, the comfort level of the passenger sitting on the seat in normal instances was not very good. In other words, when the passenger sits back towards the seat back (seat back frame), the space between an upper rim part of the upper pelvis supporting unit and a lower rim part of the chest part supporting unit became concaved. As a result, the passenger will feel a concaved and convex terrain on the seat back. Therefore, there is a problem in that, when the passenger sits on the seat, the passenger may feel uncomfortable.